$namespcae: 'xz' !default;
$black-sel: '-' !default;
$elem-sel: '__' !default;
$mod-sel: '--' !default;

@mixin bfc {
  height: 100%;
  overflow: hidden;
}

@mixin b($block) {
  $B: #{$namespcae + $black-sel + $block};

  .#{$B} {
    @content
  }
}

@mixin e($el) {
  $selector: &;

  @at-root {
    #{$selector + $elem-sel + $el} {
      @content;
    }
  }
}

@mixin m($m) {
  $selector: &;

  @at-root {
    #{$selector + $mod-sel + $m} {
      @content;
    }
  }
}